Useful Methods

The following is a list of methods commonly used in Objectdraw, Greenfoot, BlueJ, or possibly all three. Feel free to add, make corrections, or improve the organization of this page.


yourVariable.getX(); returns the x coordinate of an object (Objectdraw)

yourVariable.getY(); returns the y coordinate of an object (Objectdraw)

yourVariable.getWidth(); returns the width of an object (Objectdraw)

yourVariable.getHeight(); returns height of an object

yourVariable.setWidth(amount); sets the width of your object to the given amount

yourVariable.setHeight(amount); sets the height of your object to the given amount

yourRand.nextValue(); assigns the next value for a random number

yourObject.setColor( new Color ( #, #, #)); changes the color of an object to whatever you want using rgb

yourObject.setColor(Color.red);

yourVariable = scan.nextInt();

yourObject.move(x, y); moves an object a set amount x and y units away from initial coordinates

yourObject.moveTo(x, y); moves an object to new coordinates

getRotation();

setLocation(#, #);

setRotation(x);

delay(); (greenfoot)

getRandomNumber(); (greenfoot) works the same way as random generator

boolean isKeyDown(String keyName); (greenfoot)

drawLine(x1, y1, x2, y2); (greenfoot)

Math Functions

1. Math.sqrt(x) gives square root of value
2. Math.pow(x, y) this would be x to the power of y
3. Math.exp(x) e to the power of x
4. Math.min(x, y) finds the smaller value of the two
5. Math.max(x, y) finds the larger of the two values
6. Math.sin(x) finds the sine of x, when x is in radians
7. Math.cos(x)
8. Math.tan(x)
9. Math.toRadians(x) converts degrees to radians
10. Math.toDegrees(x) //converts radians to degrees

// *************************************************************
//   Distance.java
//
//   Computes the distance between two points
// *************************************************************
 
import java.util.Scanner;
import java.util.Random;
 
 
public class Distance
{
    public static void main (String[] args)
    {
    double x1, y1, x2, y2; // coordinates
 
    Scanner scan = new Scanner(System.in);
    Random generator = new Random();
 
 
    System.out.print ("Enter the X and Y coordinates of the first point; press enter in between coordinates.");
    x1 = scan.nextDouble();
    y1 = scan.nextDouble();
 
    System.out.print ("Enter the X and Y coordinates of the second point: ");
    x2 = scan.nextDouble();
    y2 = scan.nextDouble();
 
    // Compute the distance
    double sumOfSquares = Math.pow((x1 - x2), 2) + Math.pow((y1 - y2), 2);
    double distance = Math.sqrt(sumOfSquares);
 
 
    }
}
 

To drag and object in BlueJ with your cursor:

Location lastMouse;   //make sure this is under the public class
                       //it creates the location of the cursor so you can
                        //drag the object
 
public void onMousePress(Location point)
{
     lastMouse = point;      //it makes the point your mouse clicks the
                              //the first point
}
 
public void onMouseDrag(Location point)
    {
        double changeX = point.getX() - lastMouse.getX();
        double changeY = point.getY() - lastMouse.getY();
        object.move(changeX,changeY);
        object2.move(changeX,changeY);
        lastMouse = point;
    }                          //it gets the x and y of the primary point your
                               //cursor was at when you made the location
                               //point and the x and y of the point your cursor
                               //is at now. The changeX and Y are the
                               //differences. The object moves the difference
                               //and the point it is now is stored as the
                               //primary point.